summat

What is this?

Ofttimes, during the process of the usage of TypeScript, one may encounter the following behaviour:

interface A {
	a?: X
}

const a: A = {}
a.b = 33 // TypeError: Property 'b' does not exist on type 'A'

The solution to this is well known and documented:

interface A {
	a?: X
	[x: string | number | symbol]: any
}

const a: A = {}
a.b = 33 // ok

However, repeating the exact same line, over and over, and over again (particularly so, in larger applications) may be quite daunting indeed!

This is precisely what the Summat interface is for:

interface Summat {
	[x: string | number | symbol]: any
}

interface A extends Summat {
	a?: X
}

const a: A = {}
a.b = 33 // ok

Installation

npm install @hgargg-0710/summat.ts

The module provides the following exports (types):

interface Summat<Type = any> {
	[x: string | symbol | number]: Type
}

Note: useful for adding optional objects to interfaces/object-types;

type SummatFunction<This = any, In = any, Out = any> = Summat &
	((this: This, ...args: In[]) => Out)

Note: useful for creation of types for functions with properties

type SummatIterable<Type = any> = Iterable<Type> & Summat